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What exactly is a zero carbon home then Gordon?

by Mel Starrs on December 7, 2006

in Zero Carbon

Gordon Brown announced his pre-budget report yesterday. The pertinent chapter for our industry is Chapter 7 (pdf, 26 pages). Driving home last night Radio 4 were asking the question ‘what is a zero carbon home?’. The reporter had even rang up DCLG for an answer – a spokesman said “one which was not a net recipient of electricity from the national grid” but it was clear that the reporters were still somewhat confused. We could wait for the Code for Sustainable Housing (due for publication next week, I believe) for the official definition but I believe what follows will be close.

The commonly cited definition of zero carbon development comes from the London Renewables document, ‘Towards Zero Carbon Developments‘ (pdf, 108 pages):

A zero carbon development is one that achieves zero net carbon emissions from energy use on site, on an annual basis.
Excluded in this definition are embodied energy in construction and demolition and transport energy. This is the simplest definition, although arguably not the most ‘green’ option available. A better definition would be:
A zero carbon house is one that approaches net carbon emissions from energy use in construction and on site over the useful life of the building
There are of course a number of issues with this definition, which I don’t believe the industry is quite ready for yet (but should be by 2016).
Firstly, the embodied energy in building materials and items such as PV panels, boilers etc is still not widely quoted. BRE have developed a methodology (Ecopoints (pdf, 2 pages) which the Envest tool uses) but uptake has not been widespread as there is no current driver. This would be the perfect opportunity to move this initiative forward.
There are some in the industry who seem to believe this will be included in Gordon’s plans – see this article regarding timber framed buildings. Some interesting statistics in there (although they come from UK Timber Frame Association (UKTFA) so possibly not totally impartial). I agree entirely with the essence of what they are saying, but I do think this a some way off realising yet.
The second point with my definition above is what is deemed ‘the useful life of the building’. The government in their own capital expenditure projects tend to use 60 years. Our housing legacy in the UK is currently a mixed bag with Victorian terraces outliving sixties council blocks by 50 years or more. Shorter periods of time would render many of the renewables which are currently in vogue unfeasible if the embodied energy is taken into account.
All this is supposition at this point in time – by next week it should all become clear.